Exposure Assessment and Air Toxics by wwq52447

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									Exposure Assessment
and Air Toxics
               Ken Mitchell, Ph.D.
               U. S. EPA Region 4
                   Atlanta, GA

                 June 23, 2002
The mission of the U.S.
Environmental
Protection Agency is to
protect human health
and to safeguard the
natural environment--
air, water, and land--
upon which life
depends.

EPA's purpose is to
ensure that:

All Americans are
protected from
significant risks to
human health and the
environment where
they live, learn and
work…                     2
Lots of things are “risky!”




                              3
Risk from Exposure to Contaminated Air




                                         4
Exposure at different scales
?   What is our inhalation exposure to toxic
    chemicals of concern in our Region (at a
    “screening level of concern”)?
?   What is our inhalation exposure to toxic
    chemicals of concern in our community (at
    a“ high level of concern”)?




              National/State
                                  Community
                 County
                                    Level
                  Level                         5
Air Toxics - Why are they
potentially so risky?
?   May cause cancer or other serious
    health effects in people or the
    environment
?   May disperse locally to globally
?   Potential to be persistent and/or
    bioaccumulate in the food chain
?   Potential for multi-media exposure
?   188 compounds (hazardous air
    pollutants) listed in the Clean Air
    Act
    – 33 NATA priority chemicals
    – 21 mobile source HAPs               6
Air Toxics Emissions
are decreasing… ..




                                                                                                        … but there is
                                                                                                            still work
                                                                                                                 to do.


USEPA (2001) National Air Quality and Emissions Trends Report, 2999, OAQPS (EPA 454/r-01-004), March.
                                                                                                                      7
                                       NATA - National Scale Assessment
                                    Predicted County Level Carcinogenic Risk




          Median Risk Level

            <1 in a Million
            1 - 25 in a Million
            25 - 50 in a Million
            50 - 75 in a Million
            75 - 100 in a Million
            >100 in a Million




Courtesy of Ted Palma/OAQPS.
                                                                               8
USEPA (2001) National Air Quality and Emissions Trends Report, 2999, OAQPS (EPA 454/r-01-004), March.
                                                                                                        9
    t
Don’ forget indoor air quality!




  Indoor air can be many times more
  polluted than outdoor air and we
  usually spend more time indoors…    10
What are doing about air toxics?
              ?   Multiple programs
                  and initiatives
                  – Technology and risk-
                    based standards
                    (MACTS, residual
                    risks)
                  – Mobile source
                    programs
                  – Special Initiatives
                     • Deposition studies
                     • Urban Strategy
                     • International transport   11
The Risk Assessment
& Risk Management
Paradigms                  Hazard
                        Identification



                        Dose/Response
                         Assessment




                          Exposure
                         Assessment



                             Risk
                        Characterization


Risk Management       Risk Assessment
    Paradigm             Paradigm
                                           12
What is chemical “exposure?”
?   The literature has various
    definitions for the point on or in
    the body where exposure takes
    place.
?   Human exposure usually means
    contact with the chemical or agent,
    but this could mean contact with:
     – The visible exterior of the
        person (skin and openings into
        the body such as mouth and
        nostrils), or
     – The exchange boundaries
        where absorption takes place
        (skin, lung, gastrointestinal
        tract).

     USEPA (1992), Guidelines for Exposure Assessment, 57 FR 22888.   13
EPA defines “exposure” as...
?   Contact with the visible
    exterior of the person
     – Skin
     – Mouth
     – Nostrils
     – Punctures in the skin
?   USEPA (1992),
    Guidelines for Exposure
    Assessment, 57 FR
    22888.                     14
                                               Transport,
                                                Mixing,
                                               Reactions




     es
  urc
So



                                                                           Wet/Dry Deposition,
                                                                            Reevaporation,
                                                                            Reentrainment




          Penetration
           Indoors
                                   Direct
                                 Inhalation,
                                   Dermal                Bioaccumulation
                                                        in/on Human Food




                        Soil/Water/Sediment
                               Dermal,
                              Ingestion

                                                                                        15
Intake and Uptake are Different!

?   Intake - Physically
    moving a chemical
    through an opening
    in the boundary into
    the body (usually
    mouth or nose)
?   Uptake - Absorption
    across the boundary
    (usually skin or eye)

                                   16
Dose is different too!
?   Applied (or potential) dose
     – Amount of a chemical at the absorption
        barrier (skin, lung, gastrointestinal tract)
        available for absorption.
?   Internal Dose
     – The amount of a chemical that has been
        absorbed and is available for interaction
        with biologically significant receptors
?   Delivered Dose
     – The amount transported to an individual
        organ, tissue, or fluid of interest
?   Biologically Effective Dose
     – The amount that actually reaches cells,
        sites, or membranes where adverse effects
        occur
                                                       17
Example – Respiratory Route


                                                  Biologically
Chemical                                           Effective
               Potential   Applied   Internal
                                                     Dose
Exposure        Dose        Dose       Dose


                                                  ORGAN          EFFECT
                                     metabolism




       Mouth/Nose               Lung


           INTAKE              UPTAKE


                                                                  18
“Exposure Assessment”
?   Quantitative or Qualitative assessment of
    contact which usually describes:
    – Intensity, frequency, duration of contact
    – Rates at which the chemical crosses the
      boundary
    – Route of exposure (inhalation, dermal, etc.)
    – Amount of chemical that crosses the
      boundary (potential dose)
    – Amount absorbed (absorbed dose)


                                                     19
Exposure Assessment for Air Toxics
?   Usually evaluate
    inhalation route of
    exposure
?   “Indirect”routes of
    exposure are important
    for some chemicals that
    deposit on soil or water
    (e.g., dioxin, mercury)
    – Ingestion of Hg-laden
      fish
    – Eating lead-laden soils
                                 20
Exposure Assessment
?   Characterize the exposure setting
    – Physical environment including the scale
      of the study area
    – Potentially exposed populations
?   Identify exposure pathways
    – Exposure point
    – Exposure route
?   Quantify exposure
    – Exposure concentration
    – Intake variables
?   You must have a complete exposure
    pathway for there to be a risk               21
How do we estimate “exposure” & risk?


  Risk =
   Intake x (Toxicity) =

   (C)(CR)(EF)(ED) x (Toxicity)
      (BW)(AT)


  Where: C is concentration, CR is contact rate, EF is
         exposure frequency, ED is exposure
         duration, BW is body weight, AT is averaging
         time, and “Toxicity”is a factor that describes
         the toxic potential (dose/response) of a
         chemical                                     22
For inhalation, this usually
solves to… .
 Risk = C/IUR           (for carcinogens)


 Hazard = C/RfC         (for noncarcinogens)


  Where: IUR is inhalation unit risk; and
           RfC is reference concentration
           ***(Tox values are usually from IRIS)


              WE WANT “C”                          23
How do we determine C… ?
?   Chronic Exposure
    – Low level exposure over an extended
      period of time
?   Usually C is developed to be
    representative of long term
    concentration (e.g., annual
    average)
    – Modeling (ISC3, CalPuff,
      Aermod, etc.)
    – Monitoring (1 in 6 day ambient
      samples for a year, personal
      monitoring, etc.)
?   C can reflect activity patterns
    – HAPEM4, APEX                          24
How do we determine C… ?
?   Acute Exposure
    – High level exposure over a short period of time
?   C can also reflect short term exposures (15
    minutes, 1h, 24h, 2 weeks)
?   Chronic and Acute effects are often different




                                                        25
C and measures of toxicity are
interrelated
?   Our underlying assumptions
    about C should match the
    underlying assumptions about
    the toxicity factor we match it
    with when calculating risk
    –   Cancer
    –   Chronic noncancer
    –   Acute noncancer
    –   Reproductive &
        developmental

                                      26
Cumulative exposure is
important...
?   There are usually multiple
    sources in an impacted
    area… transport into an airshed
    may also be important
?   Source by source assessment
    may significantly underestimate
    risk
?   Tools and guidance are being
    developed
    – RAIMI
    – Framework for Cumulative Risk
      Assessment                      27
                         Exposure Assessment at Different Scales
                                              Source Oriented
                                              Assessments
                        400
                                                                       Urban Area
                                                                      Assessments
                                                                                                 National Scale
                        350                                                                      Assessments




                        300
                                                                                               Predicted Downwind
                                                                                                  Concentration
Concentration (ug/m3)




                        250



                        200



                        150
                                                                                                   NATA Census
                              Typical Point                                                        Tract Centroid
                                 Source
                        100
                                               Maximum Exposed
                                                                 Local Community
                                                 Individual at
                                                   Fenceline
                         50



                          0


                                                                                    Distance
                                                                                                    elibrative Document for Internal OAQPS Use Only

                                                                                                                                                      28
Exposure Assessment at Different Scales



                  National/State
                                              Community
                     County
                                                Level
                      Level




                                                    Organ Level
   Neighborhood
       Level                       Personal                   29
                                    Level
Exposure Assessment at Different Scales
?   Screening level of assessment on a large
    geographic scale
    – NATA ASPEN modeling
    – Limited national air toxics “trends”monitors
?   Refined analysis at a smaller geographic
    scale
    – Personal monitoring, microenvironments
    – Intensive monitoring/modeling/emissions
      inventory at the community level
    – Assessment of activity patterns in a particular
      place
    – Pharmacokinetic models
?   Assessment goals drive the data
    requirements                                        30
Exposure Assessment at
Different Scales
?   Screening level assessment at low
    geographic resolution usually provides lower
    certainty estimates of risks to receptors in
                                       big
    specific communities (this is the “ picture”   )
?   Refined analysis at high geographic (or
    personal or biological) resolution usually
    provide higher certainty about risks to specific
    receptors in specific places
?   “Certainty”at any scale depends on the tools
    and inputs used in the particular assessment
                                                  31
In summary…
 ?   Exposure vs. exposure assessment
 ?   Calculating “exposure” and risk
     – Modeling vs. Modeling
     – Chronic vs. Acute
     – Attention to toxic endpoints
 ?   Scale is important
 ?   Uncertainties exist at every point
     along the way




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